1. Field of the Invention
This invention relates to hydraulic lifters to be used in a valve train of internal combustion engines and more particularly to improved hydraulic lifters incorporated into the rocker arm in the valve train of overhead cam (OHC) type.
2. Discussion of the Background
The conventional structure of a hydraulic lifter incorporated into the rocker arm of the valve train of the internal combustion engine is disclosed, for example, in the Japanese Patent Laid-open Publication No. 16112/1978. In this conventional hydraulic lifter, a lifter body is inserted into a hole formed in the rocker arm and a plunger is arranged slidably in the cylinder formed in said lifter body. A reservoir chamber for storage of working fluid is formed in the plunger and the plunger is provided with a partition wall separating the reservoir chamber from a pressure chamber. Since the reservoir chamber is provided in the plunger and the partition wall having a check valve seat is integrally formed into the plunger, the plunger cannot avoid being large in order to secure a reservoir chamber which takes a relatively large volume. This increases the overall size of the hydraulic lifter as well as the inertial mass of the valve train, resulting in a drawback in that the operating range of the engine rotation decreases. Another problem is that the manufacturing costs increases because of the complex shape of the plunger.